GPASSWD

NAME

SYNOPSIS

DESCRIPTION

The
gpasswd
command is used to administer
/etc/group, and /etc/gshadow. Every group can have
administrators,
members and a password.

System administrators can use the
-A
option to define group administrator(s) and the
-M
option to define members. They have all rights of group administrators and members.

gpasswd
called by
a group administrator
with a group name only prompts for the new password of the
group.

If a password is set the members can still use
newgrp(1)
without a password, and non-members must supply the password.

Notes about group passwords

Group passwords are an inherent security problem since more than one person is permitted to know the password. However, groups are a useful tool for permitting co-operation between different users.

OPTIONS

Except for the
-A
and
-M
options, the options cannot be combined.

The options which apply to the
gpasswd
command are:

-a, --adduser

Add the
user
to the named
group.

-d, --deleteuser

Remove the
user
from the named
group.

-h, --help

Display help message and exit.

-Q, --rootCHROOT_DIR

Apply changes in the
CHROOT_DIR
directory and use the configuration files from the
CHROOT_DIR
directory.

-r, --remove-password

Remove the password from the named
group. The group password will be empty. Only group members will be allowed to use
newgrp
to join the named
group.

-R, --restrict

Restrict the access to the named
group. The group password is set to "!". Only group members with a password will be allowed to use
newgrp
to join the named
group.

-A, --administratorsuser,...

Set the list of administrative users.

-M, --membersuser,...

Set the list of group members.

CAVEATS

This tool only operates on the
/etc/group
and /etc/gshadow files.
Thus you cannot change any NIS or LDAP group. This must be performed on the corresponding server.

CONFIGURATION

The following configuration variables in
/etc/login.defs
change the behavior of this tool:

ENCRYPT_METHOD (string)

This defines the system default encryption algorithm for encrypting passwords (if no algorithm are specified on the command line).

It can take one of these values:
DES
(default),
MD5, SHA256, SHA512.

Note: this parameter overrides the
MD5_CRYPT_ENAB
variable.

MAX_MEMBERS_PER_GROUP (number)

Maximum members per group entry. When the maximum is reached, a new group entry (line) is started in
/etc/group
(with the same name, same password, and same GID).

The default value is 0, meaning that there are no limits in the number of members in a group.

This feature (split group) permits to limit the length of lines in the group file. This is useful to make sure that lines for NIS groups are not larger than 1024 characters.

If you need to enforce such limit, you can use 25.

Note: split groups may not be supported by all tools (even in the Shadow toolsuite). You should not use this variable unless you really need it.

MD5_CRYPT_ENAB (boolean)

Indicate if passwords must be encrypted using the MD5-based algorithm. If set to
yes, new passwords will be encrypted using the MD5-based algorithm compatible with the one used by recent releases of FreeBSD. It supports passwords of unlimited length and longer salt strings. Set to
no
if you need to copy encrypted passwords to other systems which don't understand the new algorithm. Default is
no.

This variable is superseded by the
ENCRYPT_METHOD
variable or by any command line option used to configure the encryption algorithm.

This variable is deprecated. You should use
ENCRYPT_METHOD.

SHA_CRYPT_MIN_ROUNDS (number), SHA_CRYPT_MAX_ROUNDS (number)

When
ENCRYPT_METHOD
is set to
SHA256
or
SHA512, this defines the number of SHA rounds used by the encryption algorithm by default (when the number of rounds is not specified on the command line).

With a lot of rounds, it is more difficult to brute forcing the password. But note also that more CPU resources will be needed to authenticate users.

If not specified, the libc will choose the default number of rounds (5000).

The values must be inside the 1000-999,999,999 range.

If only one of the
SHA_CRYPT_MIN_ROUNDS
or
SHA_CRYPT_MAX_ROUNDS
values is set, then this value will be used.

If
SHA_CRYPT_MIN_ROUNDS
>
SHA_CRYPT_MAX_ROUNDS, the highest value will be used.